WO2016185828A1 - Image formation method - Google Patents

Abstract

This image formation method is a method in which a halftone image is formed on a cardboard recording medium by an inkjet recording device in which magenta ink and two or more inks of other colors besides magenta ink are used, wherein the method is efficient in that after the position where magenta ink is to impact has been decided, the impact positions of the two or more inks of other colors are decided so as to be different from the magenta ink impact position, whereby mottling does not occur in an image printed in multiple colors on the cardboard recording medium by the inkjet recording device.

Description

Image forming method

The present invention relates to an image forming method, and more particularly, to an image forming method for forming a halftone image on a cardboard recording medium using an ink jet recording apparatus.

It is known that when multicolor printing is performed on a recording medium using an inkjet recording method, image degradation called mottle occurs. This phenomenon is caused by the fact that water exceeding the amount of water that can be absorbed by the recording medium is contained in the ink used in the ink jet recording apparatus. As a result, the ink moves on the recording medium, resulting in the density of the pigment.

In order to suppress such a mottle, a technique for providing a time difference when each ink is ejected (Patent Document 1) and a technique for changing the ink ejection position for each color (Patent Document 2) have been proposed. Yes.

Japanese Patent Application Laid-Open No. H10-228867 discloses that different ink dots are formed on a medium by an ink jet recording apparatus having an ink nozzle row for each ink that forms ink dots on the medium and a control unit that controls the ink ejection operation. In this case, it is disclosed that the timing at which each ink is ejected is changed so as to suppress bleeding and color mixing of the image.

In Patent Document 2, halftone processing using a dither method is performed on each color plate data obtained by converting each color plate data of CMYK to a resolution of 1 / n (n is an integer of 2 or more) of the output resolution. Replace the dot pattern of the plate data with a dot pattern corresponding to the color material usage reduction rate, and change the replaced dot pattern between color plates so that the dots of each color do not overlap. Therefore, it is disclosed to suppress bleeding.

JP 2012-61781 A JP 2013-66082 A

In recent years, with the advancement of inkjet printing technology, multicolor printing on corrugated cardboard recording media has replaced the so-called analog printing using conventional flexographic plates, and the introduction of inkjet printing digital printing.
It is known that the above-mentioned mottle is generated even when printing is performed on a cardboard recording medium by an ink jet recording method. However, in the techniques disclosed in Patent Documents 1 and 2, it is formed on a cardboard recording medium. There is a problem that the motor of the generated image cannot be sufficiently solved and it takes time to output the image.

SUMMARY OF THE INVENTION An object of the present invention is to provide an efficient image forming method that eliminates the problems of the prior art and does not cause mottle in an image printed on a cardboard recording medium using an ink jet recording apparatus. It is in.

In order to achieve the above object, according to the image forming method of the present invention, a halftone image is formed on a corrugated cardboard recording medium by an ink jet recording apparatus using two or more colors other than magenta ink and magenta ink. An image forming method comprising:
After the magenta ink droplet ejection position is determined, the droplet ejection positions of other inks of two or more colors are determined so as to be different from the magenta ink droplet ejection position.

Here, the ink droplet ejection positions of two or more colors are different from the printing positions of magenta ink droplets ejected at a predetermined pitch on a corrugated cardboard recording medium and other ink droplets of two or more colors. It is preferable to be determined as follows.
Further, the droplet ejection positions of other inks of two or more colors can be determined so that the droplet ejection positions of inks having different color materials are different positions.
Here, it is preferable that the droplet ejection positions of other inks of two or more colors are determined so that the printing positions of the ink droplets of different color materials that are ejected at a predetermined pitch on the corrugated cardboard recording medium are different. .
In addition, the ink droplet ejection positions of other inks of two or more colors can be determined to be the same position.

Here, after determining a magenta ink droplet ejection position and a droplet ejection position of other inks of two or more colors, a magenta ink halftone pattern having a predetermined pitch is determined using a dither matrix, and then magenta It is preferable to determine halftone patterns of other inks of two or more colors having a predetermined pitch so as to fill a predetermined area of the dither matrix to which no ink halftone pattern is assigned.
The predetermined area of the dither matrix to which the magenta ink halftone pattern is not assigned is an area included in an area where the magenta ink halftone pattern and the halftone pattern of two or more other colors overlap. This is the position on the dither matrix when the droplet ejection position where the magenta ink dots are not printed on the halftone pattern is projected onto the dither matrix of another ink of two or more colors.
In order to determine the droplet ejection positions of other inks of two or more colors, a dither matrix is used so that ink droplets of different color materials of two or more colors of other inks deposited on the cardboard recording medium overlap. Is preferably used to determine halftone patterns of other inks of two or more colors.

In order to determine the droplet ejection positions of other inks of two or more colors, the dither matrix is set so that the print positions of different inks of different color materials of the two or more colors ejected onto the cardboard recording medium are different. Is preferably used to determine halftone patterns of other inks of two or more colors.
In order to determine the droplet ejection positions of other inks of two or more colors, it is preferable to determine a halftone pattern of other inks of two or more colors preferentially from an ink with a high visual density using a dither matrix.

A magenta ink halftone pattern and two or more ink halftone patterns are half-pitched using a dither matrix to determine the magenta ink ejection position and the ink ejection positions of two or more colors. It is preferable to determine the halftone pattern of magenta ink and other inks of two or more colors so as to be shifted.

The ink jet recording apparatus includes a magenta nozzle array in which a plurality of nozzles that eject magenta ink are arranged at a predetermined pitch in the main scanning direction and at equal intervals, and a plurality of nozzles that eject other inks of two or more colors for each color material And a recording head comprising two or more other ink nozzle rows arranged at a predetermined pitch at regular intervals in the main scanning direction, and the two or more other ink nozzle rows are arranged in the main scanning direction or the sub-scanning direction with respect to the magenta nozzle row. It is preferable to have a recording head arranged with a half-pitch shift in the operation direction.

According to the present invention, when multicolor printing is performed on a corrugated cardboard recording medium using an ink jet recording method, an image without mottle can be easily formed.
Further, according to the present invention, it is possible to easily and efficiently generate an image pattern of each color that is printed in multiple colors on a cardboard recording medium.

It is a block diagram which shows an example of the image forming method which concerns on 1st Embodiment. It is a figure for demonstrating the term "predetermined pitch". It is a figure which shows the state where "the droplet ejection position is different" and the state where "the droplet ejection position is the same". It is a figure which shows a "print position is different" state and a "print position is the same" state. It is a graph which shows each usage-amount and total ink amount of CMYK ink used when reproducing 18 colors defined by JCS (cardboard industry standard) by inkjet printing. It is a figure for demonstrating the printing pattern which concerns on 1st Embodiment. It is a figure which shows an example of the printing pattern which concerns on 1st Embodiment. It is a flowchart which shows the halftone processing method which concerns on 1st Embodiment. It is a figure which shows the determination order of the halftone pattern which concerns on 1st Embodiment. It is a figure for demonstrating the determination method of the halftone pattern of each color which concerns on 1st Embodiment. It is a figure for demonstrating the determination method of the halftone pattern of each color which concerns on 1st Embodiment. It is a figure for demonstrating the determination method of the halftone pattern of each color which concerns on 1st Embodiment. It is a figure which shows an example of the printing pattern which concerns on 2nd Embodiment. It is a flowchart which shows the halftone processing method which concerns on 2nd Embodiment. It is a figure for demonstrating the determination order of the mask pattern of each ink which concerns on 2nd Embodiment. It is a figure for demonstrating the determination method of the halftone pattern of each color which concerns on 2nd Embodiment. It is a figure for demonstrating the determination method of the halftone pattern of each color which concerns on 2nd Embodiment. It is a figure for demonstrating the modification of the determination order of the mask pattern of each ink which concerns on 2nd Embodiment. It is a flowchart which shows the halftone processing method which concerns on 3rd Embodiment. It is a figure for demonstrating the determination method of the halftone pattern of each color which concerns on 3rd Embodiment. 1 is a block diagram illustrating a configuration of an ink jet recording system according to first to third embodiments. FIG. It is a block diagram which shows the structure of the halftone process part shown in FIG. It is a figure which shows the structure of the recording head which concerns on 4th Embodiment.

Hereinafter, an image forming method according to the present invention will be described in detail with reference to preferred embodiments shown in the accompanying drawings.
[Embodiment 1]
FIG. 1 is a diagram illustrating an example of an image forming method according to the first embodiment of the present invention.
In the image forming method of the present invention, a color image is acquired as RGB data, and M (magenta), C (cyan), Y (yellow), and K (black) color materials (ink) are recorded on a cardboard recording medium. A halftone image is recorded by a printing apparatus (inkjet recording apparatus) based on an inkjet recording system that ejects droplets at a predetermined pitch.

First, in step S10, image data (RGB data) output by the inkjet recording apparatus is acquired.
Next, in step S12, the acquired RGB data is converted into image data of each of three colors of MCYK, for example, MCY, MCK, MYK, or four colors of MCYK.

Next, in step S16, halftone processing is performed on the image data after the color conversion processing to determine a halftone pattern (mask pattern) for each color.
Here, the halftone pattern of each color to be determined is a halftone image formed by superimposing, that is, a halftone processed image, an ink ejection position of M ink, and ink excluding M ink, that is, , K ink, Y ink, and C ink are determined to be different from each other.

Here, the term “predetermined pitch” used in the present embodiment will be described with reference to FIGS. 2A and 2B show droplets (dots) on which a predetermined ink is ejected while moving the recording medium in the sub-scanning direction. A square lattice (4 × 4) in the figure is 1 Represents a pixel.
When forming dots as shown in FIG. 2A, “predetermined pitch” means the distance between the centers of adjacent droplets, the sub-scanning direction pitch is “vertical pitch”, and main scanning. The pitch in the direction is called “lateral pitch”.
As shown in FIG. 2B, when a droplet is formed on the square lattice of FIG. 2A rotated 45 degrees, the “predetermined pitch” means the main scanning direction or the sub-scanning direction. Is the distance between the droplets adjacent to each other in the sub-scanning direction, the “vertical pitch” is the distance between adjacent droplets in the main scanning direction, and the “lateral pitch” is the distance between the dots adjacent in the main scanning direction. .

Further, the expression “the droplet ejection positions are different / identical” used in the present embodiment will be described with reference to FIGS. 3 (A) and 3 (B). 3A shows a state where “the droplet ejection positions are different”, and FIG. 3B shows a state where “the droplet ejection positions are the same”.
First, as a premise, the “droplet ejection position” is an ink on an image subjected to halftone processing (halftone processing), that is, on binary (or ternary, quaternary) image data. This is the position designated to print drops. 3 (A) and 3 (B) show pixels (x0, y1), (x1, y1) determined at a predetermined pixel pitch (“pitch” shown in the drawing) on the halftone-processed image. A state in which cyan and magenta are ejected on either (x0, y0) or (x1, y0) is shown.

In the state where the droplet ejection positions are different, the state where the ink droplet ejection positions are formed at different pixel positions on the halftone-processed image, that is, as shown in FIG. A state where droplets are ejected to (x0, y1) and (x1, y0) and magenta is ejected to (x0, y0) and (x1, y1).
On the other hand, the “same droplet ejection position” state is a state where the ink droplet ejection position is formed at the same pixel position on the halftone-processed image, that is, FIG. 3B shows. As described above, cyan and magenta are not ejected to (x0, y0) and (x1, y1), and cyan and magenta are ejected to (x0, y1) and (x1, y0). A state of color development.
In FIGS. 3A and 3B, cyan and magenta are used as ink droplets, but the ink is not limited to these inks as long as they are different color materials.

The expression “printing positions are different / same” used in the present embodiment will be described with reference to FIGS. 4 (A) and 4 (B). 4A shows a state where “the printing positions are different”, and FIG. 4B shows a state where the “printing positions are the same”.
First, as a premise, the “print position” refers to a position where ink droplets exist on the recording medium.
The expression “printing position is different” refers to a state in which the center of gravity of each droplet formed on the recording medium exists in different pixel areas determined at a predetermined pixel pitch, As shown in FIG. 4A, the centroids G of the cyan droplet and the magenta droplet are present in different pixel regions (pixel regions determined by the vertical pitch and the horizontal pitch in the drawing). State.
On the other hand, the expression “the printing position is the same” refers to a state in which the center of gravity of each droplet formed on the recording medium exists in the same image area determined by a predetermined pixel pitch. As shown in FIG. 4B, the centroids G of the cyan droplet and the magenta droplet are in the same pixel region (the pixel region determined by the vertical pitch and the horizontal pitch in the drawing). The state that exists.
In FIGS. 4A and 4B, cyan and magenta are used as ink droplets, but the ink is not limited to these inks as long as they are different color materials.

Such image forming conditions have been found by the present inventors conducting intensive research on image formation on a corrugated cardboard recording medium using an ink jet recording method and finding out the following contents. .

As described above, when multicolor printing is performed on a cardboard recording medium using an ink jet recording apparatus, an image having a mottle is generated. However, in general, the corrugated cardboard printing is selected from 18 colors specified by the color standard (JCSM 0001: 2000) printed on the corrugated cardboard specified as the industry standard (JCS) of the Japan Corrugated Cardboard Industry Association. There is a situation where printing is performed to reproduce the colors to be printed. Therefore, the present inventors have used C ink, M ink, Y ink and K ink used for reproducing 18 kinds of colors in ink jet printing on a cardboard recording medium, and total ink. When the amount was examined, a result as shown in FIG. 5 was obtained. The vertical axis in FIG. 5 indicates the amount of ink used and the total ink amount, and the horizontal axis indicates the 18 types of color names defined by JCS and their code numbers.

From the results shown in FIG. 5, the inventors have shown that when reproducing colors related to the regions shown in (A) to (C) in FIG. In addition, as shown in the following (1) to (4), it was found that the amount of CMYK ink used is uneven.
That is, (1) the total amount of ink when printing C ink and Y ink simultaneously is small, and (2) when printing M ink and Y ink simultaneously, as shown in area (A) in FIG. There are cases where the total ink amount is large. (3) As shown in the area (B) in FIG. 5, there are cases where the total ink amount is large when printing M ink and C ink simultaneously. As shown in the area (C) in FIG. 5, the total ink amount may be large when printing M ink, Y ink, and K ink at the same time, and the printing rate of Y ink and K ink is 100% in total. It was found that the amount of ink used for M ink is relatively large compared to the amount of ink used for Y ink and K ink.

In addition, the present inventors have further conducted intensive research and, based on the knowledge of (2) above, formed a halftone image so that the printing positions of M ink droplets and other ink droplets of two or more colors are different. Thus, it has been found that if ink is easily absorbed into the corrugated cardboard recording medium, it is possible to realize an image that suppresses generation of mottle and suppresses deterioration of graininess as much as possible. That is, as shown in FIG. 6 (A), the droplet ejection positions of M ink and Y ink are different, and from the knowledge of (3) above, droplet ejection of M ink and C ink as shown in FIG. 6 (B). As shown in FIG. 6C, the positions of the inks are different, and the positions where the M ink and Y and K ink are ejected are different, and the positions where the Y ink and K ink are ejected are different. It was found that it is preferable to form a halftone.
Details of the halftone processing method found in this way will be described later.

Finally, in step S18, a halftone image is formed on the recording medium by the ink jet recording apparatus based on the image signal of the halftone pattern of each color determined by the halftone process, and the image formation according to the present embodiment is performed. The method ends.

Next, the above-described halftone process in step S16 will be described in detail with reference to FIGS.
Here, halftone processing in ink jet printing using MKY ink will be described.
FIG. 7 is an example of a print pattern printed on a recording medium by the ink jet recording apparatus in the present embodiment. In the figure, dots indicated by shading indicate magenta (M), dots indicated by diagonal lines indicate yellow (Y), and dots indicated by sanding indicate black (K). Here, magenta dots and dots of other colors (black dots and yellow dots) are formed so that the printing positions are different. That is, magenta dots and other color dots (black dots and yellow dots) have different droplet ejection positions on the halftone image. Black dots and yellow dots are formed so that the printing positions are the same.

FIG. 8 shows a flowchart of the halftone processing method according to the present embodiment, and FIG. 9 is a diagram for explaining the order of determining the halftone pattern of each color. 10 to 12 are diagrams for explaining a method for determining a halftone pattern of each color.

First, after completion of the color conversion process in step S12, first, in step S20, one dither matrix S suitable for image data (MYK image data) as shown in FIG. 10A is determined. This dither matrix S has a threshold pattern of 4 rows × 4 columns, and integers 1 to 16 are randomly arranged as threshold values, and the threshold values of the dither matrix S are written. The portion (threshold portion) that corresponds to the ink corresponds to the droplet ejection position of the ink ejected from the inkjet nozzle. Further, a droplet (dot) formed by being ejected from an ink jet nozzle and ejected onto a recording medium corresponds to a size that satisfies this one threshold value portion.
Note that the matrix (pixel pattern) shown here is represented by a 4 × 4 pixel pattern of 16 gradations, but this is an example, and this represents the gradation of the halftone image. Since it is determined accordingly, a matrix of 8 × 8 (64 gradations) or 16 × 16 (256 gradations) can be used.

Next, in step S22, a magenta (M) halftone pattern as shown in FIG. 9A is determined.
As shown in FIG. 10A, the threshold value of the dither matrix S is compared with the signal value (10) of the image data of magenta (M) to determine the magenta (M) halftone pattern. This magenta (M) halftone pattern has a dither matrix S printed with a threshold portion of 10 or less.

Next, in step S24, colors other than magenta as shown in FIGS. 9B and 9C, that is, black and yellow halftone patterns are determined.
In this step, the order of determining the halftone patterns of colors other than magenta is not particularly limited. First, referring to FIGS. 10B to 10D, a black (K) halftone color other than magenta is used. A method for determining a tone pattern will be described.

First, as shown in FIG. 10B, a signal value (14) obtained by adding a signal value (10) of magenta (M) image data to a signal value (4) of black (K) image data is set to X. As shown in FIG. 10C, the X signal value (14) is compared with the threshold value of the dither matrix S, and a halftone pattern corresponding to the X signal value, that is, magenta, is generated. A halftone pattern in which (M) and black (K) are overlapped is determined. The halftone pattern corresponding to the signal value of X is printed with a threshold portion of 14 or less of the dither matrix S. Next, as shown in FIG. 10D, the halftone pattern corresponding to the X signal value is compared with the magenta (M) halftone pattern to determine the black (K) halftone pattern. This black (K) halftone pattern is obtained by erasing the X signal value where magenta (M) is printed in the halftone pattern corresponding to the X signal value.

Next, a method for determining a yellow (Y) halftone pattern will be described with reference to FIGS. The yellow (Y) halftone is determined by a method similar to the method for determining the black (K) halftone pattern.
That is, as shown in FIG. 11A, a signal value (16) obtained by adding a signal value (10) of magenta (M) image data to a signal value (6) of yellow (Y) image data is set to X. As shown in FIG. 11B, the Y signal value (16) is compared with the threshold value of the dither matrix S to generate a halftone pattern corresponding to the X signal value, that is, magenta. A halftone pattern in which (M) and yellow (Y) are overlapped is determined. The halftone pattern corresponding to the signal value of X has a threshold value portion of 16 or less of the dither matrix S printed thereon. Next, as shown in FIG. 11C, the halftone pattern corresponding to the X signal value is compared with the magenta (M) halftone pattern to determine the yellow (Y) halftone pattern. This yellow (Y) halftone pattern is obtained by erasing the X signal value where magenta (M) is printed in the halftone pattern corresponding to the X signal value.

In this manner, image data for determining magenta, black and yellow halftone patterns as shown in FIGS. 9A to 9C is formed. That is, a halftone image is formed in which the droplet ejection positions of magenta dots and the droplet ejection positions of other color dots (black dots and yellow dots) are different.
When ink is deposited on the recording medium based on the halftone image formed here, a print pattern as shown in FIG. 7 is formed. That is, the printing positions of magenta dots and other color dots (black dots and yellow dots) are different, and the same image is formed at the printing positions of black dots and yellow dots.

In the above-described embodiment, as shown in FIG. 10B and FIG. 11A, the signal value (10) of the image data of magenta (M) is added to the signal value (4) of the image data of black (K). ) And the signal value of X calculated by adding the signal value (10) of the image data of magenta (M) to the signal value (6) of the image data of yellow (Y) to the yellow (Y) image data. Although the case where the signal value is equal to or less than the maximum threshold value (16) of S is shown, a case where the signal value exceeds the maximum threshold value (16) of the dither matrix S is also assumed. In such a case, black (K) and yellow (Y) halftone patterns are determined by the method described below.

As shown in FIG. 12A, the signal value (20) generated by adding the signal value (10) of magenta (M) image data to the signal value (10) of black (K) image data, The signal value (16) that is the maximum threshold value of the dither matrix S is the X signal value, and the remainder (4) is the A signal value.
Next, as shown in FIG. 12B, the threshold value of the dither matrix S is compared with the X signal value (16) to determine the halftone pattern corresponding to the X signal value. The halftone pattern corresponding to the signal value of X has a threshold value portion of 16 or less of the dither matrix S printed thereon.

Next, as shown in FIG. 12C, the halftone pattern corresponding to the X signal value is compared with the magenta (M) halftone pattern determined in FIG. In the halftone pattern corresponding to the value, the halftone pattern Z in which the Y signal value at the place where magenta (M) is printed is deleted is determined.

Next, as shown in FIG. 12D, the threshold value of the dither matrix S is compared with the signal value (4) of A to determine the halftone pattern B. In this halftone pattern B, a threshold portion of 4 or less of the dither matrix S is printed.
Next, as shown in FIG. 12E, the halftone pattern Z and the halftone pattern B are compared to determine a black (K) halftone pattern. This black (K) halftone pattern is obtained by overlapping the halftone pattern Z and the halftone pattern B.

This black (K) halftone pattern has a threshold portion that overlaps with the magenta (M) halftone pattern, and the overlapping threshold portion is mixed with ink. That is, the black (K) ink and the magenta (M) ink may have a portion where both droplets overlap on the recording medium, that is, the printing position may be the same. However, according to the halftone creation method shown in FIGS. 12A to 12E, the threshold portion where magenta (M) and black (K) overlap is minimized, that is, the liquid of magenta (M) ink. A black (K) halftone pattern can be created in which the overlap between the droplets and the black (K) ink droplets is minimized.

The same applies when the value obtained by adding the signal value (10) of the magenta (M) image data to the signal value (6) of the yellow (Y) image data exceeds the maximum threshold 16 of the dither matrix S. The method can determine a yellow (Y) halftone pattern.

In the present embodiment, the case where MKY ink is used for inkjet printing has been described. However, the present invention is not limited to this, and the color and type of ink used for inkjet printing may be other colors as long as magenta is used. Is not particularly limited, and known colors, types, and numbers of inks can be used. For example, magenta and cyan, yellow or black ink are used, magenta and cyan and yellow, or cyan and black ink are used, magenta, black, yellow and cyan. It is also possible to use four inks.

In this embodiment, the ink droplet ejection positions are different from each other. However, the black (K) ink and yellow (Y) ink ejection positions are the same, and the predetermined positions on the cardboard recording medium are set. It is also possible to overlap ink droplets of different color materials printed at a pitch. That is, the droplet ejection positions of magenta (M) ink and the droplet ejection positions of black (K) ink and yellow (Y) ink are different, but the droplet ejection positions of black (K) ink and yellow (Y) ink are the same. The black (K) ink and the yellow (Y) ink can be printed at the same position.
The recording medium is not particularly limited as long as it is a corrugated cardboard recording medium. For example, cardboard called a K liner or a C liner is preferably used.

[Second Embodiment]
In the first embodiment, as shown in FIG. 7, a plurality of ink droplets excluding magenta, that is, half-tones of each color so as to form a print pattern in which black (K) dots and yellow (Y) dots overlap. The tone pattern has been determined, but preferably, as shown in FIG. 13, the ink droplets of different color materials, that is, the overlap of black (K) dots and yellow (Y) dots is minimized. The halftone pattern of each color can also be determined so that ink droplets of different color materials, that is, a print pattern in which black (K) dots and yellow (Y) dots do not overlap at all.

FIG. 14 is a flowchart of the halftone processing method according to the present embodiment, and FIG. 15 is a diagram for explaining the order of determining the halftone pattern of each color.

First, similarly to the first embodiment, after completion of the color conversion processing in step S12, in step S30, first, one dither suitable for image data (MKY image data) as shown in FIG. A matrix S is determined.

Also in the subsequent step S32, a magenta (M) halftone pattern as shown in FIG. 15A is determined by the same method as in the first embodiment. That is, as shown in FIG. 10A, the threshold value of the dither matrix S is compared with the signal value (10) of the image data of magenta (M) to determine the magenta (M) halftone pattern.
In this way, after the magenta (M) halftone is determined, the halftone pattern is determined in the order of colors having the highest visual density.

In step S34, a color having a high visual density among colors other than magenta is determined. In this embodiment, a black (K) halftone pattern as shown in FIG. 15B is determined. Also in step S34, a black (K) halftone pattern is determined by the same method as in the first embodiment. That is, as shown in FIGS. 10B to 10D and FIGS. 12A to 12E, a black (K) halftone pattern is determined.

Next, in step S36, a color having a low visual density among colors other than magenta, that is, a yellow (Y) halftone pattern as shown in FIG. 15C is determined. That is, the yellow (Y) halftone pattern is determined so as not to overlap with the previously determined magenta (M) and black (K) halftones.
An example of a method for determining the yellow (Y) halftone pattern will be described with reference to FIGS. 16 (A) to (C) and FIGS. 17 (A) to (B).

As shown in FIG. 16A, the signal value (4) of black (K) image data and the signal value of yellow (Y) image data (10) are added to the signal value (10) of magenta (M) image data. In the signal value (20) generated by adding 6), the signal value (16) which is the maximum threshold value of the dither matrix S is defined as the W signal value, and the remainder (4) is defined as the A signal value.

As shown in FIG. 16B, the threshold value of the dither matrix S is compared with the W signal value (16) to determine the halftone pattern corresponding to the W signal value. The halftone pattern corresponding to the W signal value has a threshold portion of 16 or less of the dither matrix S printed thereon.
As shown in FIG. 16C, the halftone pattern corresponding to the W signal value is compared with the magenta (M) halftone pattern. In the halftone pattern corresponding to the W signal value, the M ink is present. The halftone pattern Z from which the W signal value at the place to be printed is erased is determined.

As shown in FIG. 17A, the threshold value of the dither matrix S is compared with the signal value (4) of A to determine the halftone pattern B. In this halftone pattern B, a threshold portion of 4 or less of the dither matrix S is printed.
As shown in FIG. 17B, the halftone pattern Z and the halftone pattern B are compared to determine a yellow (Y) halftone pattern. This halftone pattern is obtained by overlapping the halftone pattern Z and the halftone pattern B.

The yellow (Y) halftone pattern has a threshold portion that overlaps with the magenta (M) and black (K) halftone patterns. That is, the yellow (Y) ink, the magenta (M) ink, and the black (K) ink may have a portion where both droplets overlap on the recording medium, that is, the print position may be the same. However, the halftone creation method shown in FIGS. 17A and 17B described above minimizes the threshold portion where yellow (Y) overlaps magenta (M) and black (K), that is, yellow (Y). A yellow (Y) halftone pattern can be created in which the overlap between the ink and the magenta (M) and black (K) ink droplets is minimized.

Thus, magenta, black, and yellow halftone patterns as shown in FIGS. 15A to 15C are determined.

In this embodiment, two colors of black and yellow are used as colors other than magenta. However, the present invention is not limited to this, and a combination of other two colors may be used, and inks of three or more colors are used. Also good. In this case, the halftone pattern is determined in order of colors with the highest visual density.

Further, in the present embodiment, after determining the magenta (M) halftone, the halftone patterns are determined in the order of colors with the highest visual density. However, the present invention is not limited to this, and as shown in FIG. ) First, the yellow (Y) halftone pattern shown in FIG. 18B is determined, and then the black (K) shown in FIG. 18C is determined. The halftone pattern may be determined.

[Third Embodiment]
In the first and second embodiments, the common dither matrix is used for the image data of each color in order to determine the halftone pattern of each color. However, the present invention is not limited to this, and magenta (M). Also, different dither matrices can be used for image data of two or more colors (X colors) excluding magenta.

An example of the halftone processing method according to the third embodiment will be described in detail with reference to FIG. 19 and FIG. FIG. 19 shows a flowchart of a halftone processing method according to this embodiment, and FIG. 20 is a diagram for explaining a method of determining a halftone pattern for each color.

First, in step S40, using a systematic dither method or the like, as shown in FIG. 20A, first, a dither matrix having a value corresponding to the number of gradations of magenta (M) is determined, and in step S42. Then, a mask pattern obtained by rotating the determined magenta (M) dither matrix by 45 degrees is arranged in a square lattice to determine a magenta (M) halftone pattern. In this pattern, magenta ink is handled so as not to be ejected at a position having no signal.

Next, in step S44, using a systematic dither method or the like, as shown in FIG. 20B, a dither matrix having values corresponding to the number of gradations of other colors (X colors) excluding magenta ink is obtained. After the determined dither matrix is rotated by 45 degrees in step S46, this mask pattern is further arranged in a square lattice, and further overlapped with the magenta ink mask pattern determined in FIG. A halftone pattern of other colors (X colors) excluding magenta is obtained by shifting one pixel each in the vertical and horizontal directions so as not to be shifted (so as to be shifted by a half pitch). In this pattern as well, it is assumed that X color ink is not ejected at a position where there is no signal.

Thus, by using different dither matrices for magenta (M) and colors excluding magenta (X color), the degree of freedom of the position where each halftone pattern is arranged increases, so that the image structure image quality (granularity) Property and sharpness) can be improved.

FIG. 21 is a block diagram of an ink jet recording system that performs the image forming method according to the embodiment. The ink jet recording system 10 includes an image forming apparatus 12 and an ink jet recording apparatus 14.
In the inkjet recording system 10, a color image is acquired as RGB data by the image data input unit 16 of the image forming apparatus 12, and the input color image is recorded on the recording medium using a plurality of inks by the image output unit 24 of the inkjet recording apparatus 14. It is to be recorded above.

The color conversion processing unit 18 converts the RGB data input from the image data input unit into image data (CKY data) of each color and outputs it. The CKY data includes magenta (M) image data, black (K) image data, and yellow (Y) image data separated for each color.

As shown in FIG. 22, the halftone processing unit 20 includes a dither matrix holding unit 26 that holds a dither matrix pattern, input image data (magenta (M) image data, black (K) image data, and A mask pattern determining unit 28 that determines a halftone pattern (mask pattern) of each color as a halftone image by performing dither matrix processing using yellow (Y) image data) using a dither matrix.
The halftone processing unit 20 stores in the dither matrix holding unit 26 the signal values included in the magenta (M) image data, black (K) image data, and yellow (Y) image data in the mask pattern determination unit 28. A halftone pattern of each color is determined by performing a comparison process with a threshold value of a dither matrix having a predetermined threshold arrangement in the main scanning direction and the sub-scanning direction and performing dither conversion. The halftone patterns of these colors determined by the mask pattern determination unit 28 are output as output image data to the drive signal generation unit 22 of the inkjet recording apparatus 14.

The ink jet recording apparatus 14 includes a drive signal generation unit 22 and an image output unit (recording head) 24 connected to the drive signal generation unit 22.
The drive signal generation unit 22 receives the halftone pattern of each color from the halftone processing unit 20 as halftone image data, and ejects the ink with an ejection amount corresponding to the image signal value of the halftone pattern. A drive signal value for driving the output unit 24 is generated.

The image output unit 24 is, for example, an ink jet recording head that ejects ink by using an expansion / contraction operation of a piezoelectric element, and ejects ink onto a recording medium to record a recording image. The recording head is not particularly limited as long as a plurality of inkjet heads in which a plurality of ink discharge nozzles are arranged in the sub-scanning direction (paper feeding direction) are arranged in the main scanning direction. Further, the color and type of ink output from the ink discharge nozzle are not particularly limited as long as magenta is used, and known colors and types of ink can be used.

The ink jet recording apparatus 14 used in the present invention is not particularly limited, and a conventionally known ink jet recording apparatus can be used. For example, the ink jet recording apparatus 14 is not particularly illustrated, but as an ink jet recording head, the ink jet nozzles of each color corresponding to the recording width (printing width) of the recording medium are arranged in one or more rows. A line head or a carriage type short ink jet head in which one or a plurality of ink discharge nozzles of each color shorter than the recording width of the recording medium are arranged may be used.

The recording medium is not particularly limited as long as it is a corrugated cardboard recording medium. For example, cardboard called K liner or C liner can be used.
The resolution of the ink jet recording apparatus is not particularly limited, but a resolution of 300 dpi or more is preferable.

Further, the present invention includes a program for causing a PC (personal computer) to execute each step of the image forming method according to the above-described embodiment and a storage medium storing the program.

[Fourth Embodiment]
In the above embodiment, the dither matrix is used to determine the magenta ink and the magenta ink that is ejected onto the corrugated cardboard recording medium by determining the halftone pattern of two or more inks other than the magenta ink. Although the method of forming the halftone image by determining the droplet ejection positions of other inks of two or more colors has been described, droplets are ejected onto a cardboard recording medium using a recording head as shown in FIG. It is also possible to form halftone images in which the droplet ejection positions of magenta ink and other inks of two or more colors are different.

20 includes a magenta nozzle row 34M in which a plurality of nozzles 32M that eject magenta ink are arranged at equal intervals in the main scanning direction, and a plurality of nozzles 32C that eject cyan ink in the main scanning direction at equal intervals. And a yellow nozzle row 34Y in which a plurality of nozzles 32Y for discharging yellow ink are arranged at a predetermined pitch at regular intervals in the main scanning direction.
The “predetermined pitch” used here indicates the distance between the nozzle hole centers of the adjacent nozzles, and the distance between the nozzle hole centers of the adjacent nozzles is shown in FIGS. The “vertical pitch” and “lateral pitch” described with reference to FIG.
The cyan ink nozzle row 34C and the yellow nozzle row 34Y are arranged with a half-pitch L shift in the sub-scanning direction with respect to the magenta nozzle row 34M.

In the above embodiment, the cyan ink nozzle row 34C and the yellow nozzle row 34Y row are arranged with a half-pitch shift in the sub-scanning direction with respect to the magenta nozzle row 34M. They may be arranged with a half-pitch shift in the direction.

The image forming method of the present invention has been described in detail with reference to various embodiments and examples. However, the present invention is not limited to these embodiments and examples, and does not depart from the spirit of the present invention. Of course, various improvements or changes may be made.

DESCRIPTION OF SYMBOLS 10 Inkjet recording system 12 Image forming apparatus 14 Inkjet recording apparatus 16 Image data input part 18 Color conversion process part 20 Halftone process part 22 Drive signal generation part 24 Image output part 26 Dither matrix holding part 28 Mask pattern determination part 30 Recording head 32M , 32C, 32Y Discharge nozzles 34M, 34C, 34Y Nozzle rows

Claims (11)

1. An image forming method for forming a halftone image on a cardboard recording medium by using an ink jet recording apparatus using magenta ink and other inks of two or more colors excluding the magenta ink,
   After the ink droplet ejection position of the magenta ink is determined, the ink droplet ejection positions of the two or more colors are determined so as to be different from the ink ejection position of the magenta ink. Method.
2. The ink droplet ejection positions of the two or more colors are the printing positions of the magenta ink droplets ejected at a predetermined pitch on the cardboard recording medium and the ink droplets of the two or more colors. The image forming method according to claim 1, wherein the image forming method is determined differently.
3. 3. The image forming method according to claim 1, wherein the droplet ejection positions of the other inks of two or more colors are determined so that the droplet ejection positions of the different color materials are different.
4. The ink droplet ejection positions of the two or more colors are determined so that the printing positions of ink droplets of different color materials that are ejected onto the corrugated cardboard recording medium at a predetermined pitch are different. The image forming method according to any one of claims 1 to 3.
5. 3. The image forming method according to claim 1, wherein the ink droplet ejection positions of the two or more colors are determined to be the same as the ink droplet ejection positions of different color materials.
6. In order to determine the droplet ejection position of the magenta ink and the droplet ejection position of the other two or more colors, a halftone pattern of the magenta ink having the predetermined pitch is determined using a dither matrix. The halftone patterns of the other two or more colors having the predetermined pitch are determined so as to fill a predetermined area of the dither matrix to which no halftone pattern of the magenta ink is assigned. Item 6. The image forming method according to any one of Items 1 to 5.
7. In order to determine the droplet ejection positions of the other inks of two or more colors, the ink droplets of different color materials of the two or more other colors that are ejected onto the corrugated cardboard recording medium overlap. The image forming method according to claim 6, wherein halftone patterns of the other inks of two or more colors are determined using the dither matrix.
8. In order to determine the droplet ejection positions of the other inks of two or more colors, the print positions of ink droplets of different color materials of the two or more other inks that are ejected onto the cardboard recording medium are The image forming method according to claim 6, wherein halftone patterns of the other inks of two or more colors are determined using the dither matrix so as to be different.
9. In order to determine the droplet ejection positions of the other inks of two or more colors, the halftone pattern of the other inks of the two or more colors is preferentially determined from the ink having a high visual density using the dither matrix. The image forming method according to claim 8.
10. In order to determine the droplet ejection position of the magenta ink and the droplet ejection position of the other two or more colors, a dither matrix is used to form the magenta ink halftone pattern and the two or more ink halftone patterns. The image forming method according to any one of claims 1 to 4, wherein halftone patterns of the magenta ink and the other inks of two or more colors are determined so as to be shifted by a half pitch.
11. The inkjet recording apparatus includes a magenta nozzle array in which a plurality of nozzles that eject magenta ink are arranged at a predetermined pitch in the main scanning direction and at equal intervals, and a plurality of nozzles that eject the other two or more colors. For each material, a recording head comprising two or more other ink nozzle rows arranged at the predetermined pitch in the main scanning direction and at equal intervals,
    10. The two or more other ink nozzle rows are arranged so as to be shifted by the half pitch in the main scanning direction or the sub operation direction with respect to the magenta nozzle row. Image forming method.

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